The present invention pertains to the electrical signal monitoring art and, more particularly, to apparatus for simultaneously monitoring multiple power carrying lines, detecting a transient condition on any line and storing data representing the waveform on the line both before and after the transient event.
The detection and analysis of disturbances on electrical power carrying lines has become an extremely important endeavor due to the widespread use of solid state computers and microprocessor based controllers. Such solid state equipment is known to be susceptible to damage, or operating fault conditions as a result of power line transients. Inasmuch as power line disturbances occur randomly and at widely spaced intervals, the study and analysis of such disturbances has proved difficult.
The present monitoring instruments for detecting power line transient disturbances include power line monitor/loggers and digital storage oscilloscopes. Conventional power line monitors are designed to detect the presence of relatively slow transient conditions, recording the time of occurrence and peak amplitude, but yielding no details on the waveform, pulse width or other patient factors of the transient. Whereas digital oscilloscopes are capable of capturing and displaying high speed transients, recording such waveforms for later analysis, they require the presence of an operator and, as such, are not well suited to the unattended monitoring of an electrical system.
An additional problem with conventional power line monitor/loggers and digital storage oscilloscopes is that they are typically not capable of monitoring several channels simultaneously. The origin of a transient condition is often not ascertainable unless several power lines are monitored simultaneously. Whereas, several individual power monitors or oscilloscopes may be provided to simultaneously monitor multiple power lines, such as exercise is expensive due to the need for redundant units.
A useful feature of a power line monitoring system is the ability to permanently store transient waveforms. Thus, it has been known to provide some form of permanent storage means, such as magnetic tape, into which may be loaded digital signals representing the waveform in question. Heretofore, power monitoring systems have operated either manually, such that an operator makes the decision to load a particular waveform into storage, or automatically, i.e., a detected transient signal is automatically transferred to permanent storage. The problem suffered by the manual systems is that they do not lend themselves to unattended power line monitoring. The fully automatic systems, on the other hand, suffer the drawback that the transient being stored in memory often yields no useful analytical information.
An additional desirable feature of a power line monitoring system is the ability to record both pre- and post trigger information. That is, such power line systems normally include a triggering device for sensing the occurrence of a transient disturbance. In oscilloscope monitoring systems, it is the presence of this transient detect signal which triggers the oscilloscope sweep. However, a full analysis of the origin of the transient may not be possible without reviewing the electrical waveform on the power line just prior to the transient. Further, post trigger waveform information is also often of use in analyzing the cause of a disturbance. The ability to capture both pre- and post trigger waveform activity is, therefore, often essential to a full analysis of the disturbance.
For power monitoring systems which are capable of monitoring multiple power lines simultaneously, system operation may be substantially enhanced if a central controller is provided to process transients stored in each channel in an orderly manner, resetting the channels to a condition for further signal reception. Absent some means for processing the data stored in each of the channels, and returning each processed channel to an active monitoring state, such a multichannel system may miss transients which occur on the monitored lines subsequent to a prior transient.
Further, in multichannel monitoring systems wherein stored transient waveforms are to be committed to permanent memory, it would be useful to provide a means for allowing an operator to select the file size of each channel memory which is to be committed to permanent storage. In this way, the processing time for each channel may be kept to a minimum and maximum use may be made of the permanent storage facility.
In addition, for monitoring systems employing analog-to-digital converters, a means for allowing an operator to select the sampling rate of each channel's converter in a multiple channel monitoring system is desirable. High frequency transient signals require a high frequency sampling rate to successfully capture the transient. However, for relatively low frequency transients, it is preferred to take samples less often, thereby preserving memory space.
A yet further desirable feature in a multiple channel power line monitoring system is the capability of channel triggering in a master/slave mode. Often, a transient on one power carrying line will produce a response on other lines. This response may not be of sufficient magnitude to trigger the detection circuitry for those other channels. As such, it would be desirable to provide a means whereby a transient in one channel causes a corresponding triggering of other selected channels, whereby the total effect of the transient disturbance may be evaluated.
Additional desired features of such power line monitoring systems include means for recording the time at which a particular disturbance occurred and, where permanent storage means are used, means for providing a backup storage, such that the backup system takes over when the primary system is fully loaded.